1. Field of the Invention
This invention relates to a method and apparatus for comminuting solid particles and more particularly to such a method and apparatus which utilizes pressurized gas to drive the particles upwardly in a chamber through rotors and rotating semipermeable screens which perform the comminuting action.
2. Description of the Related Art
Micronized limestone is used in agriculture, industrial fillers, environmental controls and the construction trade. Micronized cement is useful in the building industry.
Micronized coal is used as an energy source in the generation of electricity and micronized limestone/dolomite or lime are used for environmental compliance in the flue gas cleanup of power plants. Micronized coal burns with a flame velocity similar to natural gas or fuel oil and with a short flame that allows the heat energy generated in the combustion to be readily transferred to the water walls of the boiler. This results in an increased boiler rating and less heat losses through the ducts and flue stack. In addition to providing a more complete combustion, the micronized coal upon combustion yields a micronized fly ash with low carbon content which is of considerable value in the construction industry as a substitute for cement in high strength concrete formulations.
In addition the combustion of micronized coal requires no excess air and results in minimized NOx in the flue gases. Micronized limestone, dolomite or hydrated lime are most valuable in the dry hot scrubbing of flue gases and affords a more effective aqueous scrubbing thereof as these particles have much larger reactive surfaces for the SOx and NOx scrubbing. This results in a more complete utilization of the sorbents resulting in substantial savings in the flue gas clean up section of a power plant in conforming to the requirements of the Clean Air Act.
The use of micronized coal and limestone/dolomite or lime as the fuel for generating electric power thus has significant advantages over the use of conventional fuels such as fuel oil or non-micronized coal and is much less expensive than natural gas.
In my U.S Pat. No. 5,695,130 issued Dec. 9, 1997, a grinding system is described in which rotating screens with wide mesh openings are first used to comminute particulate material through spiral vortexes and such comminuted material is then fed to circular vortexes formed between rotating discs and stationary plates where the final grinding of the particulate material is accomplished and the final comminuted material is separated from the gas streams by centrifugal fans. The system and method of the present invention applies the basic technology of my prior patent in implementing the micronization of solid particles such as coal, limestone/dolomite, lime, and cement. The system of the present invention provides an improvement over the system of my prior patent in minimizing the erosion of the fan blades employed and lowering the system power requirements.